<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

<form action="4.post.php" method="post" >
    用户名：<input type="text" name="username" /><br>
    密码：<input type="text" name="password" /><br>
    <input type="submit" value="登录" />
</form>

</body>
</html>